Method of fabricating an MOCVD titanium nitride layer utilizing a pulsed plasma treatment to remove impurities

ABSTRACT

A MOCVD is performed to form a titanium nitride layer on the surface of a semiconductor substrate. Following that, a pulsed plasma treatment is performed to remove hydro-carbon impurities from the titanium nitride layer. Therein, the pulsed plasma treatment is performed in a pressure chamber comprising nitrogen gas (N 2 ) hydrogen gas (H 2 ) or argon gas (Ar). A pressure of the pressure chamber is controlled to between 1 to 3 Torr, with the power of the pressure chamber controlled to between 500 and 1000 watts.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of fabricating a titaniumnitride layer, and more particularly, to a method of fabricating atitanium nitride layer to reduce thermal budget of the fabricationprocess as well as to remove hydro-carbon impurities within the titaniumnitride layer.

2. Description of the Prior Art

In modern semiconductor processes, metal organic chemical vapordeposition (MOCVD) is gradually replacing the traditional sputteringprocess. The MOCVD uses metal organic compounds to form a thin metalfilm, such as tungsten (W), aluminum (Al), tantalum nitride (TaN) ortitanium nitride (TiN), or a ferroelectric film, such as BaSrTaO_(x)(BST), on a semiconductor substrate. However, using MOCVD also bringssome disadvantages. For example, hydro-carbon impurities are also formedwithin the titanium nitride layer during the deposition process of thetitanium nitride layer. As a result, the resistance of the titaniumnitride layer is increased.

Please refer to FIG. 1 and FIG. 2. FIG. 1 and FIG. 2 are schematicdiagrams of a method of fabricating a titanium nitride layer on asemiconductor wafer 10 according to the prior art. As shown in FIG. 1,the semiconductor wafer 10 comprises a silicon substrate 12, a bottomconducting layer 16 positioned on the silicon substrate 12, a dielectriclayer 18 with a low dielectric constant (low K) positioned on the bottomconducting layer 16 as an inter-metal dielectric (IMD) layer, and aplurality of plug holes 20 positioned within the dielectric layer 18(only a plug hole 20 is shown in FIG. 1). Therein, the bottom conductinglayer 16 is an aluminum wire, and an anti-reflection coating (ARC) 17 oftitanium nitride (TiN) is formed on the aluminum wire. As for the plughole 20, it is used to form a tungsten plug therein in a later process,so as to electrically connect to the bottom conducting layer 16. Thebottom conducting layer 16 functions as a gate, a source or a drain of aMOS transistor.

Following that, as shown in FIG. 2, a MOCVD is performed to deposit atitanium nitride layer 26 on the side wall of the plug hole 20, thetitanium nitride layer 26 functioning as a barrier layer. The reactionof the MOCVD can be illustrated in the following reaction equation:

Ti[N(CH₃)₂]₄→TiN(C,H)+HN(CH₃)₂+hydro-carbon impurities

As shown in the equation, after the deposition of the titanium nitridelayer 26, some hydro-carbon impurities are also formed within thetitanium nitride layer 26 by the MOCVD. As a result of the occurrence ofthe hydro-carbon impurities, the resistance of the titanium nitridelayer 26 is increased and the uniformity of the products is affected.

In order to solve the above-mentioned problems, after the MOCVD iscompleted, a plasma treatment is required to remove the hydro-carbonimpurities within the titanium nitride layer 26 and simultaneouslydensify the titanium nitride layer 26. However, the plasma treatmentencounters some problems. During the plasma treatment, the siliconsubstrate 12 is often heated to above 420° C. and aluminum within thebottom conducting layer 16 may extrude to the surface of the titaniumnitride layer 26 to affect the tungsten plug's RC value. In addition,under such a high temperature, the structure of the dielectric layer(low K IMD layer) 18 is damaged.

SUMMARY OF THE INVENTION

It is therefore a primary objective of the present invention to providea method of fabricating a titanium nitride layer to reduce thermalbudget and remove hydro-carbon impurities within the titanium nitridelayer.

It is another objective of the present invention to solve the problem ofaluminum extrusion.

It is still another objective of the present invention to prevent damageon the low K IMD layer.

According to the claimed invention, a MOCVD is used to form a titaniumnitride layer on the surface of a semiconductor substrate. After that, apulsed plasma treatment is performed to remove hydro-carbon impuritiesfrom the titanium nitride layer. Therein, the pulsed plasma treatment isperformed in a pressure chamber. The pressure chamber comprises nitrogengas (N₂), hydrogen gas (H₂) or argon gas (Ar). The pressure of thepressure chamber is controlled at between 1 and 3 Torr, and the power ofthe pressure chamber is controlled at between 500 and 1000 watts. Inaddition, a chiller is used to control temperatures cooling off thebackside of the semiconductor substrate, so as to ensure the multi-stepplasma treatment is performed with the temperature of the semiconductorsubstrate less than 390° C.

It is an advantage of the present invention that the temperature of thesemiconductor substrate is prevented from going too high, so thecharacteristics of the semiconductor elements are not destroyed. Inaddition, the thermal budget of the fabrication process is reduced andthe hydro-carbon impurities are effectively removed according to thepresent invention.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment, that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 and FIG. 2 are schematic diagrams of a method of fabricating atitanium nitride layer on a semiconductor wafer according to the priorart.

FIG. 3 and FIG. 4 are schematic diagrams of a method of fabricating atitanium nitride layer on a semiconductor wafer according to the presentinvention.

FIG. 5 is a relation diagram of time to temperature in a pulsed plasmatreatment according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Please refer to FIG. 3 and FIG. 4. FIG. 3 and FIG. 4 are schematicdiagrams of a method of fabricating a titanium nitride layer on asemiconductor wafer 50 according to the present invention. As shown inFIG. 3, the semiconductor wafer 50 comprises a silicon substrate 52, abottom conducting layer 56 positioned on the silicon substrate 52, a lowK dielectric layer 58 positioned on the bottom conducting layer 56, anda plurality of plug holes 60 positioned within the dielectric layer 58(only a plug hole 60 is shown in FIG. 3). Therein, the bottom conductinglayer 56 is a aluminum wire, and an anti-reflection coating (ARC) 57 oftitanium nitride (TiN) is formed on the aluminum wire. The low Kdielectric layer 58 functions as an inter-metal dielectric (IMD) layer.The plug hole 60, penetrating through both the dielectric layer 58 andthe anti-reflection coating 57, is used to form a tungsten plug thereinin a later process, so as to electrically connect to the bottomconducting layer 56.

Following that, as shown in FIG. 4, a MOCVD is performed to deposit atitanium nitride layer 66 to cover the surface of the plug hole 60, thetitanium nitride layer 66 functioning as a barrier layer. During theMOCVD, tetrakis dimethyl amino titanium (TDMAT) is used as a precursor.In addition, the environment in which the MOCVD is performed alsocomprises nitrogen gas, hydrogen gas, or argon gas as a reactive gas. Areaction equation expressing the MOCVD is listed as:

Ti[N(CH₃)₂]₄→TiN(C,H)+HN(CH₃)₂+hydro-carbon impurities

As shown in the equation, after the deposition of the titanium nitridelayer 66, some hydro-carbon impurities are also formed within thetitanium nitride layer 66 by the MOCVD. As a result of the hydro-carbonimpurities, the resistance of the titanium nitride layer 66 isinevitably increased. Thus, after performing the MOCVD, a pulsed plasmatreatment is required to remove the impurities within the titaniumnitride layer 66 according to the present invention.

In a better embodiment of the present invention, the pulsed plasmatreatment is performed in a pressure chamber with a pressure rangingbetween 1 to 3 Torr and a power ranging between 500 and 1000 watts. Inaddition, nitrogen gas, hydrogen gas, or argon gas is also introducedinto the pressure chamber as a reactive gas. Therein, the pulsed plasmatreatment, uses argon gas to remove the hydro-carbon impurities from thetitanium nitride layer 66, uses hydrogen gas to carry away thehydro-carbon impurities, and uses nitrogen gas to supply nitrogen intothe titanium nitride layer 66, so as to compensate nitrogen removed bythe argon gas.

While using the pulsed plasma treatment to remove impurities within thetitanium nitride layer 66, the power of the treatment and the flow ratesof the gases must be controlled. When the treatment power is greaterthan 500 watts, the flow rates of both the nitrogen gas and the hydrogengas must be controlled to between 100 and 500 sccm (standard cubiccentimeters per minute) When the treatment power of the pulsed plasmatreatment is less than 500 watts, the flow rates of both the nitrogengas and the hydrogen gas must be controlled to between 1000 and 3000sccm, so as to enhance cooling of the semiconductor wafer 50 to achievea temperature of the silicon substrate 52 less than 390° C.

Specifically, in order to prevent the temperature of the siliconsubstrate 52 from getting too high, the operation time and power of thepulsed plasma treatment are controlled. As a result, a relation diagramof the operation time (T) to the temperature (t) of the siliconsubstrate 52 in a pulsed plasma treatment is shown in FIG. 5. Therein, apower greater than 500 watts (approximately in the range between 500 and1000 watts) is used during the first period T₁, so as to control thetemperature of the silicon substrate 52 to less than 390° C., thusremoving the hydro-carbon impurities. While in the second period T₂, thepower is less than 500 watts (approximately in the range between 0 and500 watts), and nitrogen gas and hydrogen gas are introduced with ahigher flow rate to remove the hydro-carbon impurities and supplynitrogen into the titanium nitride layer 66 to compensate nitrogen thathad been removed by argon gas. As a result, the semiconductor wafer 50is cooled, and the temperature of the silicon substrate 52 is controlledto less than 390° C.

Therein, within the first period T₁, the flow rates of both the nitrogengas and the hydrogen gas range between 100 and 500 sccm. Within thesecond period T₂, the flow rates of both the nitrogen gas and thehydrogen gas range between 1000 and 3000 sccm. Subsequently, whileturning to the third period T₃ and the fourth period T₄, the flow ratesare equal to that within the first and the second periods, respectively.Similarly, the flow rates within the further periods T_(n+1) and T_(n+2)are again equal to that within T₁ and T₂, respectively.

According to the present invention, the temperature of the siliconsubstrate 52 is effectively controlled to less than 390° C. Thesituation of the semiconductor wafer 10 being heated to above 420° C.,as in the prior art, does not happen. As a result, thermal budget of thefabrication process is reduced to prevent the structure of thedielectric layer 58 (low K IMD layer) from being damaged. In addition,the titanium nitride layer 66 is densified and the hydrocarbonimpurities within the titanium nitride layer 66 are removed, thusimproving the electrical performance of the semiconductor elements.Since a chiller is positioned in the pressure chamber to control acooling temperature of the silicon substrate 52 according to the presentinvention, the pulsed plasma treatment is always performed at thetemperature less than 390° C. Hence, the temperature of the siliconsubstrate 52 is prevented from getting too high, and problems resultingfrom the high temperature of the silicon substrate 52 are prevented.

According to a second embodiment of the present invention, a multi-stepplasma treatment on the titanium nitride layer 66 is performed. Thetemperature of the silicon substrate 52 is kept less than 390° C. duringeach step of the plasma treatment, so as to remove the hydro-carbonimpurities from the titanium nitride layer 66. For example, a firstplasma treatment is firstly performed with flow rates of both thenitrogen gas and the hydrogen gas between 100 and 500 sccm. While thetemperature of the silicon substrate 52 approaches 390° C., the firstplasma treatment stops. Following that, the flow rates of both thenitrogen gas and the hydrogen gas are adjusted to between 1000 and 3000sccm. When the temperature of the silicon substrate 52 is lowered to atemperature within a safe range, the flow rates of both the nitrogen gasand the hydrogen gas are adjusted back to between 100 and 500 sccmfollowed by performing a second plasma treatment on the titanium nitridelayer 66. While the temperature of the silicon substrate 52 approaches390° C., the second plasma treatment stops. The first and second plasmatreatments are repeated until the hydro-carbon impurities are completelyremoved and the titanium nitride layer 66 is densified. In addition, achiller may be positioned in the pressure chamber to assist cooling ofthe silicon substrate 52 during the plasma treatments.

In contrast to the prior art, the method of the present invention uses apulsed plasma treatment or a multi-step plasma treatment, with higherflow rates of both nitrogen gas and hydrogen gas in the period of asmaller power. Thus, the temperature of the silicon substrate iseffectively controlled to less than 390° C. The problems resulting fromthe high temperature of the silicon substrate that occur in the priorart, are prevented.

Those skilled in the art will readily observe that numerousmodifications and alterations of the method may be made while retainingthe teachings of the invention. Accordingly, the above disclosure shouldbe construed as limited only by the metes and bounds of the appendedclaims.

What is claimed is:
 1. A method of fabricating a titanium nitride (TiN) layer on a semiconductor substrate, the method comprising: providing a semiconductor substrate; performing a metal organic chemical vapor deposition (MOCVD) process to form the titanium nitride layer on the surface of the semiconductor substrate; and providing a varying power to perform a pulsed plasma treatment on the titanium nitride layer to remove impurities within the titanium nitride layer.
 2. The method of claim 1 wherein the metal organic chemical vapor deposition process is performed in a TDMAT (tetrakis dimethyl amino titanium)-containing environment.
 3. The method of claim 2 wherein the environment further comprises nitrogen gas (N₂), hydrogen gas (H₂) or argon (Ar) gas.
 4. The method of claim 1 wherein the pulsed plasma treatment is performed in a chamber with a pressure between 1 to 3 torr, and a power between 500 to 1000 watts.
 5. The method of claim herein the chamber comprises nitrogen gas (N₂), hydrogen gas (H₂) or argon (Ar) gas.
 6. The method of claim 1 wherein the pulsed plasma treatment is performed in a chamber comprising nitrogen gas and hydrogen gas, and while the pulsed plasma treatment uses a power greater than 500 watts, flow rates of both the nitrogen gas and the hydrogen gas range from 100 to 500 sccm (standard cubic centimeter per minute), and a temperature of the semiconductor substrate is less than 390° C.
 7. The method of claim 1 wherein the pulsed plasma treatment is performed in a chamber comprising nitrogen gas and hydrogen gas, and while the pulsed plasma treatment uses a power less than 500 watts, flow rates of both the nitrogen gas and the hydrogen gas range from 1000 to 3000 sccm.
 8. The method,of claim 1 wherein the chamber comprises a chiller to control temperature by cooling off the backside of the semiconductor substrate, so that the semiconductor substrate has a temperature less than 390° C.
 9. The method of claim 1 wherein the impurities within the titanium nitride layer comprise hydro-carbon impurities, and the titanium nitride layer functions as a barrier layer.
 10. A method of removing hydro-carbon impurities within a titanium nitride (TiN) layer, the titanium nitride layer being formed on a semiconductor substrate by a metal organic chemical vapor deposition (MOCVD) process, the method comprising: positioning the semiconductor substrate within a pressure chamber; and. performing a multi-step plasma treatment on the titanium nitride layer, a temperature of the semiconductor substrate being controlled to less than 390° C., so as to remove the hydro-carbon impurities within the titanium nitride layer.
 11. The method of claim 10 wherein a pressure of the pressure chamber is controlled to between 1 to 3 torr, and a power of each step of the plasma treatment is controlled to between 500 to 1000 watts.
 12. The method of claim 10 wherein each step of the plasma treatment is performed in a nitrogen gas (N₂)-containing and hydrogen gas (H₂)-containing environment, and each step of the plasma treatment comprises: controlling flow rates of the nitrogen gas and the hydrogen gas to within a first range, the first range ranging from 100 to 500 sccm; within the first range, performing a plasma treatment on the titanium nitride layer until a temperature of the semiconductor substrate approaches 390° C.; and controlling flow rates of the nitrogen gas and the hydrogen gas to within a second range when the temperature of the semiconductor substrate approaches 390° C. the second range ranging from 1000 to 3000 sccm.
 13. The method of claim 10 wherein the metal organic chemical vapor deposition process is performed in a TDMAT (tetrakis dimethyl amino titanium)-containing environment.
 14. The method of claim 10 wherein the pressure chamber comprises a chiller to cool the semiconductor substrate.
 15. The method of claim 15 wherein the titanium nitride layer functions as a barrier layer. 